U.S. President Barack Obama said the G8 and its partners have reached a historic consensus on climate change and the reduction of greenhouse gas emissions. Thursday's announcement came at the end of two days of discussions at the G8 summit in L'Aquila, Italy.

President Obama said G8 members and their partners from the world's major emerging economies made important strides in combating climate change.

"Developing nations committed to reducing their emissions in absolute terms and for the first time, developing nations also acknowledged the significance of the two degree Celsius metric and agreed to take action to meaningfully lower their emissions relative to business as usual in the next decade or so," he said.

Meeting here in L'Aquila, all parties agreed that global temperatures should not rise by more than an average of two degrees above pre-industrial levels.

G8 members also agreed to work toward an 80 percent cut in greenhouse gas emissions by the year 2050. While developing nations have committed themselves to negotiating cuts, they have not yet agreed on specifics.

President Obama said it is also crucial that developed nations understand the concerns of developing countries and their fear that some of these measures could hamper their economic growth. That need not be, said Mr. Obama, citing economic growth and clean energy and reduction of greenhouse gases can go hand in hand. The American president acknowledged much work lies ahead.

"We made a good start. But I'm the first one to acknowledge that progress on this issue will not be easy," he said.

President Obama said no one nation caused global warming and no one country can resolve the problem. A broad global effort is crucial, he said.

"Ultimately, we have a choice. We can either shape our future or we can let events shape it for us," he added.

Mr. Obama said consensus in L'Aquila has shown which path nations here want to take.

But there has been criticism of the proposed measures, with some environmental groups saying they are not enough. U.N. Secretary-General Ban Ki-moon has said the 2050 targets are too far in the future and that more needs to be done sooner. Many analysts said tough negotiations lie ahead before the next international conference on climate change in Copenhagen in December.

Here in L'Aquila, G8 leaders and their partners continue discussions on Friday, when the top agenda items are development assistance and Africa.